Cards

Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.

Setup code

To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:

library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)

plotly_widget <- plot_ly(x = diamonds$cut) %>%
  config(displayModeBar = FALSE) %>%
  layout(margin = list(t = 0, b = 0, l = 0, r = 0))

leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
  leaflet(options = .) %>%
  addTiles()

Shiny usage

Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.

Hello `card()`

A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).

At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.

card(
  card_header(
    class = "bg-dark",
    "A header"
  ),
  card_body(
    markdown("Some text with a [link](https://github.com)")
  )
)

A header

Some text with a link

Implicit `card_body()`

If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.¹ For example, the code to the right generates HTML that is identical to the previous example:

card(
  card_header(
    class = "bg-dark",
    "A header"
  ),
  markdown("Some text with a [link](https://github.com).")
)

A header

Some text with a link.

Restricting growth

By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().

Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.

card(
  max_height = 250,
  full_screen = TRUE,
  card_header(
    "A long, scrolling, description"
  ),
  lorem::ipsum(paragraphs = 3, sentences = 5)
)

A long, scrolling, description

Lorem non nam augue elementum cubilia habitasse in? Volutpat turpis penatibus lobortis montes per dis ac hac! Habitant placerat fringilla, proin viverra, in aenean et faucibus iaculis. Integer semper dictum ac sollicitudin – fames egestas ullamcorper mollis laoreet leo. Sociosqu velit condimentum proin, sed quisque duis nam netus cursus.

Adipiscing scelerisque mattis ad – proin blandit turpis justo aenean suspendisse elementum. Euismod at non mi himenaeos, bibendum maecenas: aliquet turpis nibh porta curae mi. Neque eu risus leo litora in, quis lacinia hendrerit. Eget purus cum morbi nisi quam congue blandit, placerat phasellus, class nunc nisl. Iaculis convallis dui dapibus aliquet erat ornare suscipit ac nullam tristique.

Amet ac morbi et mi quis. Libero vulputate eu parturient phasellus platea? Donec etiam dui aliquet taciti, risus orci gravida orci tempor interdum? Purus praesent sociosqu ultricies massa pharetra sed tristique hac mollis. Cras diam magna, rutrum neque pretium nullam eget vel pellentesque elementum non morbi netus cum luctus euismod semper himenaeos porta ante pretium hendrerit.

Filling outputs

A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.

card(
  height = 250,
  full_screen = TRUE,
  card_header("A filling plot"),
  card_body(plotly_widget)
)

A filling plot

Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.

card(
  height = 275,
  full_screen = TRUE,
  card_header("A filling map"),
  card_body(
    class = "p-0",
    leaflet_widget
  ),
  card_footer(
    class = "fs-6",
    "Copyright 2023 RStudio, PBC"
  )
)

A filling map

Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.

This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.

card(
  height = 300,
  style = "resize:vertical;",
  card_header("Plots that grow but don't shrink"),
  card_body(
    min_height = 250,
    plotly_widget,
    plotly_widget
  )
)

Plots that grow but don't shrink

Troubleshooting fill

As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.

Multiple `card_body()`

A card() can have multiple card_body()s, which is especially useful for:

Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
Allowing each card_body() to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g., min_height).

For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:

card(
  height = 375,
  full_screen = TRUE,
  card_header(
    "Filling plot, scrolling description"
  ),
  card_body(
    min_height = 200,
    plotly_widget
  ),
  card_body(
    class = "lead container",
    lorem::ipsum(paragraphs = 10, sentences = 5)
  )
)

Filling plot, scrolling description

Amet nascetur vestibulum lacus senectus venenatis porttitor placerat ultricies penatibus platea nisi eget. Accumsan venenatis iaculis dapibus mattis. Odio torquent elementum velit, augue phasellus fusce nostra erat eros! Egestas sapien elementum habitant facilisi libero dapibus ornare etiam. Magna magna montes augue montes integer cras interdum eros dictum blandit tellus, elementum curae quis.

Elit nulla felis inceptos, montes habitasse at blandit. Pulvinar fusce etiam vivamus, nisl donec vulputate sem risus posuere? Feugiat nunc enim: laoreet ridiculus integer quam semper laoreet erat eleifend arcu aenean. Posuere pharetra fusce cum, eleifend nascetur hendrerit orci elementum – urna accumsan cras laoreet? Interdum convallis etiam nullam; dui platea rutrum vestibulum inceptos leo.

Ipsum erat odio augue laoreet penatibus etiam posuere, condimentum varius? Faucibus facilisis dictumst felis libero phasellus: habitant suscipit elementum tristique nec parturient turpis ut. Dis sodales fames vitae ornare orci, mauris volutpat. Donec aliquam parturient ante magna posuere, sagittis malesuada augue? Per tincidunt arcu, feugiat tempor et, primis, luctus cum turpis – porttitor lobortis feugiat cursus nascetur primis.

Adipiscing et auctor nam – varius sapien est cras gravida. Class non egestas pharetra lectus turpis viverra lobortis ante sollicitudin. Eu mi magnis non nam platea turpis a, mus luctus ad. Vel ad hendrerit auctor laoreet – ridiculus malesuada? Convallis phasellus faucibus.

Sit cubilia luctus semper semper urna dis – hendrerit hac? Ac magnis egestas, posuere tristique; quam arcu platea mollis egestas mauris. Potenti imperdiet sociosqu lectus nisl nisl! Libero netus taciti donec eget – interdum porta risus tortor mattis cubilia. Suscipit vitae facilisis ac lectus nisi, pharetra: eget tempor, odio senectus euismod placerat tortor condimentum aliquet.

Ipsum natoque molestie sed pulvinar diam, blandit vestibulum cursus feugiat torquent. Ornare turpis ante risus sodales: est varius molestie congue! Iaculis non eros faucibus platea cras habitasse mattis neque. Natoque parturient dapibus erat convallis curabitur arcu et facilisi vitae mus a. Scelerisque taciti venenatis venenatis pretium neque!

Sit neque egestas pellentesque cras sed massa leo tincidunt nec. Interdum gravida faucibus dictumst tempus fames, mus nullam habitasse! Commodo sollicitudin vulputate: imperdiet vel netus lobortis faucibus? Morbi facilisis erat taciti imperdiet: dictumst taciti faucibus ultrices. Blandit ultricies non nec ligula auctor ornare malesuada porta faucibus: ligula tristique massa vestibulum nunc vehicula, risus aliquet viverra, lacinia eros aliquam?

Dolor montes mattis donec; libero sodales habitant elementum. Torquent feugiat montes facilisis nascetur: pretium, accumsan varius nostra pretium. Torquent placerat sapien urna rhoncus curabitur pulvinar dictum torquent. Porttitor laoreet dictumst litora ullamcorper pulvinar dis volutpat duis habitant donec? Morbi cubilia sociosqu ligula lobortis vitae senectus convallis vel tortor morbi urna.

Dolor taciti laoreet nam suscipit nec urna. Varius vitae tempus morbi venenatis cubilia himenaeos sodales: mauris malesuada est parturient magna mattis. Fringilla molestie ridiculus lacus venenatis praesent torquent erat in. Fames eleifend purus et: leo curabitur habitasse? Dis massa pharetra tristique sapien vel dui dignissim consequat ornare: dapibus: vestibulum, penatibus potenti facilisis leo fusce.

Elit dapibus facilisi, quisque natoque, augue porttitor luctus egestas dictum orci! Ligula nisi ut ad massa: rhoncus non mollis consequat posuere ad. Mauris feugiat dictumst porttitor elementum, nibh cras, imperdiet congue laoreet mollis. Commodo cursus sagittis nisl vulputate; class maecenas quis ligula, potenti porttitor tristique ornare. Na ornare.

Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:

card(
  height = 350,
  full_screen = TRUE,
  card_header(
    "Filling plot, short description"
  ),
  plotly_widget,
  card_body(
    fill = FALSE, gap = 0,
    card_title("A subtitle"),
    p(class = "text-muted", "And a caption")
  )
)

Filling plot, short description

A subtitle

And a caption

Multiple columns

As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.

card(
  height = 350,
  full_screen = TRUE,
  card_header("A multi-column filling layout"),
  card_body(
    min_height = 200,
    layout_column_wrap(
      width = 1/2,
      plotOutput("p1"),
      plotOutput("p2")
    )
  ),
  lorem::ipsum(paragraphs = 3, sentences = 5)
)

A multi-column filling layout

Dolor id mus nostra felis egestas eros iaculis ut id cubilia. Phasellus proin mauris magnis nec. Scelerisque etiam sed, libero natoque hendrerit a est a vestibulum sapien sollicitudin. Scelerisque cras quisque odio venenatis nam: semper ornare dis. Molestie mi hendrerit luctus magna nam habitasse vehicula tellus parturient habitasse; proin primis mattis nulla urna dui lacinia?

Sit ultrices nibh mi rhoncus etiam. Conubia habitant velit praesent class maecenas tortor suspendisse nec sed cras etiam. Curabitur posuere vehicula cubilia sed felis habitasse purus, nullam scelerisque imperdiet. Nisi taciti congue suscipit cursus in sociis pulvinar? Lobortis varius rhoncus mollis, nulla sed facilisi penatibus.

Dolor ut nisi luctus facilisis donec etiam purus ullamcorper? Diam tempor vulputate magna, est at purus. Sociosqu hac suscipit hendrerit class inceptos, sollicitudin taciti viverra nisl commodo fames. Molestie mi nisi – per sagittis sociis viverra enim montes himenaeos. Condimentum vulputate senectus vel habitant, feugiat convallis cursus aliquam sagittis velit pulvinar potenti.

Multiple cards

layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.

layout_column_wrap(
  width = 1/2,
  height = 300,
  card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
  card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)

A filling plot

A filling map

Multiple tabs

navset_card_tab() and navset_card_pill() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav_panel() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().

library(leaflet)
navset_card_tab(
  height = 450,
  full_screen = TRUE,
  title = "HTML Widgets",
  nav_panel(
    "Plotly",
    card_title("A plotly plot"),
    plotly_widget
  ),
  nav_panel(
    "Leaflet",
    card_title("A leaflet plot"),
    leaflet_widget
  ),
  nav_panel(
    shiny::icon("circle-info"),
    markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
  )
)

HTML Widgets

Plotly
Leaflet

A plotly plot

A leaflet plot

Learn more about htmlwidgets

Sidebars

As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().

card(
  height = 300,
  full_screen = TRUE,
  card_header("A sidebar layout inside a card"),
  layout_sidebar(
    fillable = TRUE,
    sidebar = sidebar(
      actionButton("btn", "A button")
    ),
    plotly_widget
  )
)

A sidebar layout inside a card

Static images

card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.

card(
  height = 300,
  full_screen = TRUE,
  card_image(
    file = "shiny-hex.svg",
    href = "https://github.com/rstudio/shiny"
  ),
  card_body(
    fill = FALSE,
    card_title("Shiny for R"),
    p(
      class = "fw-light text-muted",
      "Brought to you by RStudio."
    )
  )
)

Shiny for R

Brought to you by RStudio.

Flexbox

Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.

card(
  card_body(
    fillable = TRUE,
    "Here's some", tags$i("inline"), "text",
    actionButton("btn1", "A button")
  ),
  card_body(
    fillable = FALSE,
    "Here's some", tags$i("inline"), "text",
    actionButton("btn2", "A button")
  )
)

Here's some inline text

That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().

card(
  height = 325, full_screen = TRUE,
  card_header("A plot with an action links"),
  card_body(
    class = "gap-2 container",
    plotly_widget,
    actionButton(
      "go_btn", "Action button",
      class = "btn-primary rounded-0"
    ),
    markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
  )
)

A plot with an action links

Here's a simple hyperlink.

In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.

card(
  height = 300, full_screen = TRUE,
  card_header(
    class = "d-flex justify-content-between",
    "Centered plot",
    checkboxInput("check", " Check me", TRUE)
  ),
  card_body(
    class = "align-items-center",
    plotOutput("id", width = "75%")
  )
)

Centered plot

Check me

Shiny

Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).

An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).

# UI logic
ui <- page_fluid(
  card(
    max_height = 200,
    full_screen = TRUE,
    card_header("A dynamically rendered plot"),
    plotOutput("plot_id")
  )
)

# Server logic
server <- function(input, output, session) {
  output$plot_id <- renderPlot({
    info <- getCurrentOutputInfo()
    if (info$height() > 600) {
      # code for "large" plot
    } else {
      # code for "small" plot
    }
  })
}

shinyApp(ui, server)

Appendix

The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.

.shiny-plot-output {
  background-color: #216B7288;
  height: 400px;
  width: 100%;
}